Reversing his past calls for a speedy exit, President Donald Trump renewed the United States' commitment Monday to the 16-year-old war in Afghanistan, declaring that U.S. troops must "fight to win." He pointedly declined to disclose how many more troops might be sent to wage America's longest war.

In a prime-time address to unveil his new Afghanistan strategy, Trump said the U.S. would shift away from a "time-based" approach, instead linking its assistance to results and to cooperation from the beleaguered Afghan government, Pakistan and others. He insisted it would be a "regional" strategy that addressed the role played by other South Asian nations - especially Pakistan and its tolerance of the Taliban.

"America will work with the Afghan government as long as we see determination and progress," Trump said. "However, our commitment is not unlimited, and our support is not a blank check."

Still, Trump offered few details about how progress would be measured. Nor did he explain how his approach would differ substantively from what two presidents before him tried unsuccessfully over the past 16 years.

Although Trump insisted he would "not talk about numbers of troops" or telegraph military moves in advance, he hinted that he'd embraced the Pentagon's proposal to boost troop numbers by nearly 4,000, augmenting the roughly 8,400 Americans there now.

"We will ask our NATO allies and global partners to support our new strategy, with additional troop and funding increases in line with our own. We are confident they will," Trump said. His comments were echoed by Defense Secretary Jim Mattis, who said in a statement that several of those allies had joined the U.S. in committing to boost troop levels.

While Trump stressed his strategy was about more than just the military, he was vague on other aspects. He offered no specifics on ensuring Afghanistan's economic development or on securing a new diplomatic partnership in the region.

Yet on one point - the definition of victory - Trump was unequivocal. He said American troops would "fight to win" by attacking enemies, "crushing" al-Qaida, preventing terror attacks against Americans and "obliterating" the Islamic State group, whose affiliate has gained a foothold in Afghanistan as the U.S. squeezes the extremists in Syria and Iraq.

Trump's definition of a win notably did not include defeating the Taliban, the group whose harboring of al-Qaida led the U.S. to war in Afghanistan in the days after the 9/11 attacks. Like President Barack Obama before him, Trump conceded that any solution that brings peace to Afghanistan may well involve the Taliban's participation.

"Someday, after an effective military effort, perhaps it will be possible to have a political settlement that includes elements of the Taliban in Afghanistan," Trump said.

Trump said his "original instinct was to pull out," alluding to his long-expressed view before becoming president that Afghanistan was an unsolvable quagmire requiring a fast U.S. withdrawal. Since taking office, Trump said, he'd determined that approach could create a vacuum that terrorists including al-Qaida and the Islamic State could "instantly fill."

At its peak, the U.S. had roughly 100,000 there, under the Obama administration in 2010-2011. Trump said the American people are "weary of war without victory."

"I share the America people's frustration," Trump said at the Army's Joint Base Myer-Henderson Hall, in Arlington, Virginia, across the Potomac River from the White House. Still, he insisted that "in the end, we will win."

Trump's speech concluded a months-long internal debate within his administration over whether to pull back from the Afghanistan conflict, as he and a few advisers were inclined to do, or to embroil the U.S. further in a war that has eluded American solutions for the past 16 years. Several times, officials predicted he was nearing a decision to adopt his commanders' recommendations, only to see the final judgment delayed.

The Pentagon has argued the U.S. must stay engaged to ensure terrorists can't again use the territory to threaten America. Afghan military commanders have agreed, making clear they want and expect continued U.S. military help. But elected officials in the U.S. have been mixed, with many advocating against sending more troops.

As a candidate, Trump criticized the war and said the U.S. should quickly pull out, but he also campaigned on a vow to start winning wars. Exiting now, with the Taliban resurgent, would be impossible to sell as victory.

"I think there's a relative certainty that the Afghan government would eventually fall," said Mark Jacobson, an Army veteran and NATO's former deputy representative in Kabul.

And while Trump has pledged to put "America First," keeping U.S. interests above any others, his national security advisers have warned that the Afghan forces are still far too weak to succeed without help. That is especially important as the Taliban advance and a squeezed Islamic State group looks for new havens beyond Syria and Iraq. Even now, Afghan's government controls just half the country.

As officers advocated for the troop increase, the Pentagon did not claim it would end the conflict. But military officials maintained it could help stabilize the Afghan government and break a stalemate with the Taliban.

The setting for Monday night's speech, Joint Base Myer-Henderson Hall, sits alongside Arlington National Cemetery, the final resting place for many Americans who have died in the war.